The present invention generally relates to an improved system and method for servicing messages between device controller nodes and control applications (i.e. control applications) via a Lon Network. More particularly, an improved system and method for servicing messages between device controller nodes and control applications via a Lon Network, wherein the device controller nodes include a plurality of network variables for defining parameters of the Lon Network.
Supervisory and control systems for buildings have become ever more complex and sophisticated to the extent that computer networks are employed that provide control to many systems within a building or multiple buildings, such as Heating, Ventilation, & Air Conditioning systems (“HVAC”), security and fire systems, as well as energy utilization and other systems. There is a trend toward the use of open architecture in this field so that building owners can more easily and economically add to or modify such systems without being limited to that which is offered by a single manufacturer.
One network solution that has enjoyed increasing use is LonWorks® (“Lon Network”) created by EMC Engineers, Inc. The Lon Network uses Network Variables (“NV”) to expose and exchange process values between distributed nodes on the network, Network variables may be designated as inputs, which receive values from the network, or outputs, which transmit values onto the network. When a Lon Network system is commissioned the network variables that are associated with one another are tied together through a procedure referred to as binding. Network variables that have been associated in this manner are referred to as Bound network variables. When the value of an output network variable changes then the new value is automatically propagated to all of the input network variables that have been previously bound to that output. Within a Lon Network system the use of bound Network Variables is the primary mechanism by which control applications communicate with one another. The types and number of NVs in each node, which is defined as a LonWorks® technology based device, are determined by the device control application code within the node. The use of the Lon Network with a HVAC control system has proven to be relatively inflexible, inefficient and difficult to update.
One problem is that the Lon Network does not provide a simple way to set a limit for the reporting of a change of value for each specific network variable. Consequently, updates are often sent without discretion on a continuous basis, even when the change of value is insignificant. In other words, the Lon Network sends out an update of the NV value no matter how small the change of value was, and this causes bandwidth to be wasted.
Still another problem is that the Lon Network does not provide a means to discriminate between the sources of an update. There is no means for a supervisory agent to exercise exclusive control over the value of a network variable that is bound to another source. To override the value of a network variable (“NV”) on the Lon Network from a system control application, the NV must not be bound to another NV on the Lon Network. The process to remove the binding, provide the override value for a period of time, then create the binding again takes a significant amount of time. Furthermore, that is especially undesirable when the system controls a variety of parameters, such as temperature or humidity, because it is likely that multiple NVs may have to be worked on at the same time. In addition, the binding information is generally stored in Flash memory which has a limited number of erase/write cycles so removing and replacing bindings effectively reduces the operational life of the device controller.
Thus, there is a need in the art for a device that overcomes one or more of the foregoing problems.